WEATHER FORECASTING

Evening Star, Issue 21823, 12 September 1934, Page 14

WEATHER FORECASTING

LECTURE ON MODERN METHODS A lecture on the modern methods of weather forecasting and incidentally the difficulties in the path of meteorologists in New Zealand was delivered to a meeting of the Otago Institute in the physics lecture room of the Otago University last evening by Dr W. A. Macky. The president of the institute (Dr C. E. Hercus) was in the chair and briefly introduced the speaker.

Dr Macky' commenced his address by tracing the growth of weather forecasting from the earlier times, when theories promulgated by Theophrastus were relied upon for close on 2,000 years owing to the absence of any definite data on which to work, until in the seventeenth century the barometer was invented and a slight advance was made. Taken by itself, however, the barometer was then, as it is now, an unreliable guide to the weather. In 1688 Halley explained the origin of-the trade winds and drew a map showing the distribution of the winds, this being probably the first weather map ever drawn. However, forecasting required a map which gave the conditions at particular places at certain times of each day, and a map under those conditions could only be drawn by collecting data over a large area. It wais, however, imperative that the data should be current, as it was useless for the purpose of forecasting if it were a day or two old. It was not possible to draw such a map until the' middle of the last century, when the electric telegraph was invented. In 1849 the first meteorological data was collected by telegraph, and two years later, at the exhibition at London, a map was drawn from data supplied from various stations, in England. At the conclusion of the Exhibition the maps, which had been prepared purely as a novelty, were discontinued, but were recommenced in •1872, and had been continued ever since. From 1854 onwards, with everincreasing scope of activities, weather reports were received daily ’in London from Prance and the other European countries, blit England, like New Zealand, was at the disadvantage of having a large body of water to the westward from whence no reports could bo obtained,*and whence all the weather approached, on account of the rotation of the earth., When wireless was invented this disability was to' some extent overcome, as in 1907 the first wireless reports from the western sea were received through the co-operation of the British Navy, and then in 1909 an organisation was built tip whereby reports were supplied by the mercantile marine over the Atlantic Ocean. Nowadays wireless was used extensively for the collection and dissemination of weather reports. The various subsidiary meteorological stations in each country collected data at international hours and forwarded their reports to the central stations, where they were correlated and broadcast. All the reports were plotted on a chart and isobars were drawn showing the atmospheric pressure over various parts of the country. Previously forecasts were based, on the observation of low-pressure areas, but during the Great War the international system was dislocated, the Allies and the Central Powers keeping their information to themselves, while the neutral countries had nothing. The Norwegians, however, commenced to extend their meteorological service enormously, and as the result of their observations proved that sudden changes of wind took place more frequently than had previously been thought. The cold air from the Poles and the warm air from tlie Equator met between the thirtieth and fiftieth degree of latitude in each hemisphere, and from this the Norwegians evolved the polar front theory, which was the basis of all modern weather forecasting. When the warm dir struck the cold current it caused a Wave' in the latter, and, being lighter, broke through and was condensed, to create rain on what was known as the warm front. This process caused the cold air to come down on the opposite side of the atmospheric wave to create a'cold front, and it was from observation of these fronts that meteorologists obtained data which enabled them, to predict future weather conditions. Their movements corresponded closely to the movements of a sea wave, and their passage could he plotted from information received from ships at sea and meteorological stations on land.

. .Dr Macky showed a series of slides indicating the passage of a number ot fronts across the Tasman Sea towards New Zealand, their character changing during their progress until the Southern Alps caused further complications by introducing a fresh factor into the atmospheric process. Tlie lecturer explained, however, .that these charts had been plotted some time after the fronts had passed New Zealand, as the present system of weather reports prevented tlie dominion meteorologists from securing sufficient information beforehand to enable them to trace the progress of a front before it reached New Zealand. The last they' heard of a front was when it left the New South Wales coast, as there was not a sufficient piimber of ships’ reports to determine its location before it arrived at New Zealand. Cold fronts in these .latitudes created thunderstorms, which produced the static heard in radio sets, and endeavours were being made to secure equipment, similar to the wireless direc-tion-finders used by ships, which would enable meteorologists to determine the position of these cold fronts. Dr Macky also dealt wjth the value of accurate weather reports for aircraft, and concluded by expressing thanks to the Government meteorologist (Dr Kidson) for the loan of the slides used during the lecture'. Mr Jorgen \Holmhol, the meteorologist attached to the Lincoln Ellsworth Antarctic expedition, who had been collaborating with Dr Kidson in Wellington during the past seven months, explained the evolution of the polar front theory into the present system of determining the approach of bad weather by the presence of warm and cold fronts, and expressed the conviction that New Zealand, despite tlie handicaps under which it laboured at present by reason of the meagre reports it received from the Tasman Sea, would eventually have a valuable and efficient weather forecasting service. Dr Macky and Mr Holmhol were both heartily applauded at the conclusion of their remarks.